If you want, you can attach the cape part separately from the dress. Simplicity 2777 looks promising, view A. You would want to take in the sleeves a bit. I would use something heavier than gauze or crinkle chiffon, though (as recommended by the pattern).

If you want, you can attach the cape part separately from the dress. Simplicity 2777 looks promising, view A. You would want to take in the sleeves a bit. I would use something heavier than gauze or crinkle chiffon, though (as recommended by the pattern).

I'm using this pattern to make the dress, and I believe it's working well!
Thank you so much for you advice.

Does anyone know how I can go about making the wings at the sides of her head?

Craft foam and fabric. Or card stock and fabric. Or heavy fabric like felt. You could even use feathers.
Make a pattern out of paper to determine the size, then use it to trace and cut your chosen materials. Remember to flip the pattern for the other wing. You can attach the wings via toupee clips (do a Google search if you don't know what they are). Her wings appear to have two layers, so you may want to attach two thin layers of fabric covered card stock.
I hope this gives you some ideas...good luck!

I would suggest looking up how some people do the ears for Chii from Chobits for the wings also. Chii has some outfits from Tsubasa that have the ears look like they are fuzzy or wings, so maybe something along those lines might help as well.